1. Field of the Invention
The present invention relates to a tape speed determining apparatus in a reproducing apparatus for reproducing a video signal recorded in a recording medium such as a magnetic tape or the like. Particularly, the present invention relates to a tape speed determining apparatus for automatically determining the recording mode selected from a plurality of recording modes on which the speed of a magnetic tape depends, whereby an appropriate reproducing tape speed can be selected. More particularly, the present invention relates to an improvement of a tape speed determining circuit in a reproducing apparatus of a helical scanning system and a rotating head system, using a so-called pilot signal system for reproducing a signal recorded on a magnetic tape where tracking pilot signals are recorded in an overlapping manner with a video signal without any tracks for recording a tracking control signal.
2. Description of the Prior Art
A tracking control method using a so-called pilot signal system is proposed in the U.S. Pat. No. 4,297,733.
As an example of a video signal reproducing apparatus in which such a tracking control method of the pilot signal system is adopted, a small-sized magnetic recording and reproducing apparatus called an "8mm VTR" has attracted special interest recently. In such a small-sized magnetic recording and reproducing apparatus, a video tape can be recorded and reproduced with standardized two kinds of tape speed, namely, the standard play speed and the long play speed which is decreased to half of standard play speed for recording for a longer period of time. Accordingly, at the time of reproduction, it is necessary to determine at which tape speed the video signal has been recorded so that the video signal may be reproduced at a tape speed equal to the thus determined tape speed.
In a magnetic recording and reproducing apparatus of the VHS system or the Beta system currently placed on the market, a control-track for speed control is provided on a video tape and based on a reproduced control signal detected from this control-track, an appropriate tape speed can be determined, and thus, a tape speed for reproduction can be automatically selected.
On the other hand, in the 8 mm VTR as described above where tracking control of the pilot signal system is applied, no control-track for speed control exists on a video tape to be used. Consequently, in order to automatically determine an appropriate tape speed for reproduction, it is necessary to provide a determining circuit not depending on the reproduced control signal from the control-track.
Such speed determining circuits as used in the prior art are shown for example in Japanese Patent Application Laying-Open Gazette No. 98859/1983, Japanese Patent Application Laying-Open Gazette No. 98860/1983, and Japanese Patent Application Laying-Open Gazette No. 130459/1983, etc. However, any one of the above mentioned prior art only discloses a video tape speed determining circuit in the normal form of reproduction and involves a disadvantage that such a determining circuit cannot be utilized for special forms of reproduction other than the normal form of reproduction.
Under these circumstances, the inventor of the present application proposed in the copending U.S. patent application Ser. No. 697,100 filed on Feb. 1, 1985 by the inventor of the present application, a reproducing apparatus in which an appropriate speed consistent with the recording mode can be automatically selected for reproduction of the tape by determining even in special reproduction, in what mode the video signal to be reproduced has been recorded in the magnetic tape. In this proposed reproducing apparatus, when a discontinuously recorded track is scanned for each one field by a helical scanning system, a specified reference signal is mixed in synchronism with the scanning of the central portion of the recorded track by a head so that an error output formed by pilot signals reproduced from the central portion of the track and the mixed reference signal is subjected to sample-and-hold operation. Then, a changing cycle of the output obtained by the sample-and-hold operation is counted by a frequency divided output of the capstan motor rotation detecting output and based on the count value, the recording mode can be determined.
However, in the above described copending U.S. patent application Ser. No. 697,100 entitled "Apparatus for Reproducing Magnetically Recorded Video Signal", filed Feb. 1, 1985 by the inventor of the present application, a disadvantage is involved that the circuit structure is complicated since a specified reference signal needs to be selected temporarily from the reference signals successively provided with a field period for tracking control in synchronism with the timing of sample-and-hold operation applied to an error output which is formed based on the specified reference signal and pilot signal reproduced from the central portion of a signal track at a stable output level.